NEWS FROM OUR MEMBERS - Chemical grouting for tunnel sealing and stabilization

By: ing. Bert Kriekemans, advisor for Tekinject

Early Eighties the first injections of polyurethane grouts have been introduced by some of the current experts of Tekinject Also for sealing leakages in tunnels, like the Premetro Antwerpen, NYCA subway, London underground, etc. Later also for projects like the “Big Dig” = Central Artery in Boston. These techniques have become state of the art and are now commonly used for leaking sealing in tunnels all over the world.

Some recent interesting case stories are :

METRO RIYADH, SAUDI-ARABIA

PROJECT SCOPE

During tunnel and metro construction, waterproofing problems are a common challenge. Groundwater infiltration, if not properly sealed, can cause sever structural damage over time. During construction of the metro in Riyadh, TEKINJECT was consulted to provide a solution for various sealing problems: sealing of the TBM joints, sealing of construction seams, sealing of dilatation joints, sealing of connections between tunnels and stations. Poor installation or damaged waterproofing membranes lead to failures and caused water to accumulate behind tunnel linings.

PROJECT CHALLENGES

The variety of sealing problems needed a versatile resin, that could be adjustable due to the jobsite condition of that moment: from sealing hairline cracks, to providing a durable sealing solution of moving joints. Moreover the high water pressure in the deep underground construction increased the leakages and needed an immediate action.

PROJECT SOLUTIONS

In order to address all various sealing problems at the metro of Riyadh, a very adjustable resin was necessary. Hence the acrylic resin TEKINJECT AC FLEX (+POLYMER) was chosen. Acrylic injection can be applied without major excavation, minimizing disruption to tunnel operations. The injection process can be precisely controlled, reducing waste and ensuring thorough coverage. Overall, acrylic injection provides a reliable and cost-efficient method to restore tunnel watertightness. The acrylic based injection resin, TEKINJECT AC FLEX + POLYMER is a 4 component, acrylic, injection resin with extremely low viscosity that reacts in a though, durable, but still flexible sealing that gives a long-term sealing solution.

TEKINJECT AC FLEX + POLYMER was chosen because of its:

Adjustable setting time: In some case, high water pressure needed an immediate reaction. However in case there were small cracks, a longer setting time was desired. The highly adjustable reaction time of the resin (from sec to several minutes) made this possible.

Permeation capabilities: The extremely low viscosity of the resin, allows it to penetrate deeply in the structure, sealing the finest cracks. Once cured, the acrylic gel forms a flexible, durable barrier against groundwater. It adheres well to wet surfaces, making it ideal for active leaks.

It is also chemically resistant, ensuring long term performance in harsh undergroundenvironments like high saltine ground water.

Injection of acrylic resin, type Tekinject Flex AC, behind the tunnel lining segments to seal the leakages through the segment joints.

SCHELDETUNNEL, ZEEBRUGGE/ ANTWERP, BELGIUM

PROJECT SCOPE

The TM COTU joint venture (Besix/Stadsbader Contractors/DEME infra/Jan De Nul) flooded the dry dock in Zeebrugge, where the 8 impressive Scheldt Tunnel elements were built. In total, around 800,000 m³ of water will be used to flood the dock! The tunnel elements must be completely sealed to prevent leaks during transport and after installation.

As part of the Oosterweel connection, instructed by the client Lantis, the Scheldetunnel is being constructed to improve mobility in and around Antwerp. The tunnel will close the Antwerp Ring on the north side and has a total length of 1,800 meters, with eight tunnel elements being built and placed using the ‘immersed tunnel’ method. Each tunnel element, weighing approximately 60,000 tons, were prefabricated in a dry dock in the port of Zeebrugge. In early 2025, they are transported via the North Sea and the River Scheldt to Antwerp.

PROJECT CHALLENGES

The TM COTU joint venture flooded the dry dock in Zeebrugge, where the 8 impressive Scheldt Tunnel elements were built. In total, around 800,000 m³ of water will be used to flood the dock! The tunnel elements must be completely sealed to prevent leaks during transport and after installation.

PROJECT SOLUTIONS

To ensure complete waterproofing of the tunnel elements, TEKINJECT PU 1C FLEX 55 injection resin was applied to critical zones where fine cracks or potential leakage points were present. (cold joints, construction joints, stress cracks) TEKINJECT PU 1C FLEX 55 is a one-component, hydrophobic PU based injection resin with extremely low viscosity. Thanks to this low viscosity, the product could penetrate and seal even the smallest cracks up to 0.2 mm. The semi-flexible nature of the cured resin provides a long-lasting seal capable of withstanding structural movement and varying pressure conditions. Injection works were performed by C3K Bouwchemie and all leaks have been sealed before the departure of the elements to Antwerp.

TEKINJECT PU 1C FLEX 55 was chosen because of its:

Extremely low viscosity: Enables injection into very fine cracks (as small as 0.2 mm).

Hydrophobic properties: Reacts with water to form a closed-cell foam, ensuring a watertight seal.

No shrinkage after curing: Guarantees a permanent seal without volume loss.

Excellent adhesion: Bonds well to mineral-based construction materials such as concrete, steel and cement.

Adjustable reaction time: The reaction time can be tailored to site-specific conditions by

modifying the catalyst ratio.

Scheldetunnel segments ready to be floated while being injected from the inside with Tekinject PU C Flex